The Republican replacement plan for Obamacare just narrowly cleared the House — but the bill will almost certainly face more skepticism in the Senate.

The House GOP passed its bill by a 217-to-213 margin on Thursday, sending it to the Senate after a swift process. A series of last-minute amendments won over enough wary conservative and moderate Republicans for the plan to get approved.

But even before the divisive proposal passed the House, several Republicans in the Senate signaled that it could see major revisions. Reports also indicated that the chamber could write its own version of a bill, further complicating the yearslong effort to repeal the law.

GOP Sen. Bob Corker of Tennessee told MSNBC on Thursday morning that there is "zero chance" the bill will go unchanged in the Senate.

"I don't see any way that it goes back [to the House] in the form that it comes," he said.

The timeline on a Senate vote is unclear, but Corker indicated Thursday that the bill could spend at least a month in the chamber.

Smaller majority for GOP in Senate

Republicans hold a narrower majority in the Senate — 52 out of 100 seats — and would need a majority vote to pass the bill. Some moderate and conservative Republicans have been wary of the plan since the House introduced it earlier this year.

Some Republican senators have raised concerns about its rollback of the Medicaid expansion, which the nonpartisan Congressional Budget Office (CBO) cited in its estimate that 24 million more people would be uninsured in the next decade under the GOP plan. Others criticized its potential effect on older Americans, whose premiums are expected to rise under the plan.

GOP Sen. Rand Paul of Kentucky has argued the bill does not go far enough to repeal Obamacare, calling it "Obamacare Lite."

Many of those issues stirred concerns even before amendments, including one that allowed states under some conditions to waive the Obamacare requirements to cover essential health benefits or guarantee that people with pre-existing conditions will not see premiums spike.

Republican Sens. Lamar Alexander of Tennessee and Roy Blunt of Missouri signaled the chamber could write its own version, Bloomberg reported. GOP Sen. Lisa Murkowski of Alaska also said Thursday that she hoped to start with a "clean slate" in the Senate, according to Bloomberg.

The amended House plan has not yet been scored by the CBO to assess its costs or effects on people's coverage. That raised concerns for Republican Sen. Lindsey Graham of South Carolina.

Getty Images

Sen. Lindsey Graham

He tweeted Thursday that the bill "should be viewed with caution" because it was "finalized yesterday" and "has not been scored."

GOP Sen. Rob Portman of Ohio said in a statement that he supports changes to the health-care system, but they "must be made in a way that does not leave people behind," according to NBC News.

"I've already made clear that I don't support the House bill as currently constructed, because I continue to have concerns that this bill does not do enough to protect Ohio's Medicaid expansion," he said.

Republicans can afford only two defections to pass a bill, assuming all the Democrats and the two independents in the Senate oppose it.

Assuming the bill passes the Senate, it would return in whatever modified form to the House for a vote.

Senate Minority Leader Chuck Schumer said in a statement that the bill will go "nowhere fast" in the Senate. He urged Senate Republicans to "refuse to follow their colleagues over a cliff," and to help Democrats fix the current system rather than repeal Obamacare.